The Course of Response to Focal Photocoagulation for DME

The study objective is to determine the course of changes in OCT measured macular thickness and visual acuity following a single session of focal photocoagulation for center-involved DME. The response will be evaluated separately in eyes with and without prior focal photocoagulation for DME. The purpose is to determine the proportion of eyes that continue to improve at least 5 letters in visual acuity or at least 10% in central retinal thickness after a session of focal photocoagulation. In addition, the study will explore whether any baseline factors can be identified that are predictive of the response. All subjects will have follow-up visits 8 weeks and 16 weeks post treatment. At the 16-week visit, study eyes are evaluated for change in retinal thickness and visual acuity from baseline. * Treatment is to be deferred and follow up continued if visual acuity letter score has improved by \>5 or OCT central subfield thickness has decreased by \>10% compared with baseline. * If visual acuity letter score has not improved by at least 5 and OCT central subfield thickness has not decreased by at least 10%, then the eye is classified as 'not improved' and the investigator may provide additional treatment. Follow up ends for eyes that receive additional treatment at this visit. However, if the investigator and participant elect to defer additional treatment (even if deferral criteria are not met), then follow up will continue until the study eye receives additional treatment for DME. * Eyes continuing in follow up have visits every 8 weeks (+1week) as long as there has been continued improvement in visual acuity (letter score improved \>5 ) or retinal thickness (central subfield thickness decreased by \>10%) compared with the visit 16 weeks earlier. The longest follow-up time will be 48 weeks. By providing information on the length of time during which clinically meaningful improvement occurs following focal photocoagulation, clinicians will be better able to determine when further photocoagulation or other treatments should be considered for persistent DME. Depending on the results of this study, a future randomized clinical trial will be considered comparing the more aggressive retreatment photocoagulation regimen currently serving as the standard DRCR Network approach to focal photocoagulation for macular edema with the less aggressive regimen evaluated in this protocol.